As shown in FIG. 1, a conventional boost converter 10 includes a load disconnect switch Q1 connected between a voltage input terminal VIN and an inductor L, a diode D1 connected between the inductor L and a voltage output terminal VOUT, a power switch Q2 connected between a switching node N1 and a ground terminal GND, an output capacitor COUT connected to the voltage output terminal VOUT, and voltage divider resistors R1 and R2 serially connected between the voltage output terminal VOUT and ground terminal GND to divide an output voltage VOUT to provide a feedback voltage FB, and a pulse width modulation (PWM) controller 12 switches the power switch Q2 according to the feedback voltage FB. When the boost converter 10 starts up, an enable signal Enable turns on the load disconnect switch Q1 by an inverter 14 to connect the inductor L to the voltage input terminal VIN, so as to allow the input voltage VIN being converted into the output voltage VOUT by switching the power switch 12 according to the feedback voltage FB by the PWM controller 14.
At the moment the boost converter 10 starts up, the output voltage VOUT is zero and therefore a large inductor current IL will be instantly produced that charges the output capacitor COUT, resulting in a huge inrush. On the other hand, some components of the boost converter 10 may become short circuit or open circuit, thereby damaging certain components. For example, when the voltage output terminal VOUT is short to ground, a large short circuit current will be produced that flows through the inductor L to the voltage output terminal VOUT, and may damage the inductor L. In another case, as shown in FIG. 2, if the diode D1 becomes open circuit, the inductor current IL will charge the stray capacitor Cs at the switching node N1. Because the stray capacitance Cs is very small, the voltage at the switching node N1 may be raised instantly to a very high level and thus damage the power switch Q2.
Therefore, it is desired apparatus and methods for short circuit and open circuit protection for a boost converter.